Process for preparing filamentary microtapes of labyrinthian cross section



March 5, 1968 ROMESBERG ET AL 3,372,222

PROCESS FOR PREPARING FILAMENTARY MICROTAPES OF LABYRINTHIAN CROSS SECTION Filed Aug. 6, 1965 INVENTORS. F/QgO E. Romesberg 10 Gera/O M. Har/ Z 8 BY L/oyaE. Le/e VA? United States Patent PROCESS FOR PREPARING FILAMENTARY MICROTAPES OF LABYRINTHIAN CROSS SECTION Floyd E. Romesberg and Gerald M. Hart, Midland, and Lloyd E. Lefevre, Bay City, Micln, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Continuation-impart of application Ser. No. 338,278, Jan. 2, 1964. This application Aug. 6, 1965, Ser. No. 477,909

9 (Claims. (Cl. 264-285) ABSTRACT OF THE DISCLOSURE This application discloses and claims a process for forming filamentary microtapes comprising the sequential steps of passing a fiat fused ribbon of an organic thermoplastic resinous material through restricting means of narrower width than the width of the flat ribbon while maintaining suflicient tension on said ribbon and finally withdrawing the so folded microtape from the restricting means at an angle of at least degrees from the straight line projection of the microtape passage through said restricting means.

This invention relates to a process for preparing filamentary microtapes of labyrinthian cross section from flat tapes and ribbons. More particularly, it relates to such a process which provides exceptional control of the width and denier and cross-sectional configuration of said microtapes.

This application is a continuation-in-part of U.S. Ser. No. 338,278, filed Jan. 2, 1964, and now abandoned which was a continuation-in-part of U.S. Ser. No. 30,249, filed May 19, 1960, and now abandoned.

For many applications and uses, it is desirable to have filamentary articles of other than the traditional solid cylindrical configuration. For example, flat tapes and ribbons would seem to be a suitable form for the manufacture-of many woven and unwoven fabrics and similar articles. Such tapes and ribbons provide unusually high covering power per unit of volume and thus result in fabrics of less weight and of greater flexibility than those fabrics prepared from the prior filamentary articles of cylindrical section. However, when tapes or ribbons are employed in the usual weaving operations, it is usually necessary to twist, to plait, or otherwise to change the character of the flat tape or ribbon prior to weaving. Those operations result in a filamentary article which is characterized by poor control of width, denier, and cross-sectional geometry and result in fabrics having a hand that is little better than those prepared from the conventional cylindrical filaments.

One filamentary article that is finding increasingly wide usage in many applications is a filamentary microtape that is essentially rectangular, oval, or elliptical in peripheral silhouette. In cross section, however, these useful microtapes consist of a continuous transverse section of a tape or ribbon having the edges curled or having a transverse section of the tap or ribbon folded two, three or more times back upon itself resulting, in effect, in a series of layers separated by air. This curling or folding results in a labyrinthian cross section. These microtapes of such labyrinthian section may be used directly in conventional textile operations and, when so used, are characterized in providing the high covering power per unit of volume inherent in such peripheral silhouette. In addition, these microtapes are relatively bulky due to the air spaces between the layers. The layered structure. also lessens the chance for fibrillation which is a serious problem with most oriented, polymeric articles.

These filamentary microtapes of labyrinthian cross section, when prepared from the known organic, thermoplastic, resinous materials, are of great desirability for several reasons. Tapes and ribbons from which the desired microtape may be formed are readily prepared. Thermoplastic microtapes permit such operations as thermal forming, heat sealing, embossing, calendering, and the like. However, the thermoplastic materials frequently require orientation if the optimum properties are to be achieved in the filamentary article. In many cases, it is necessary or at least desirable to the very attainment of the tape or ribbon to orient the tape or ribbon prior to fabrication. However, the oriented form of a polymer is subject to certain difiiculties, such as fibrillation, when subjected to great stress. It would be desirable to have a process for preparing filamentary microtapes of labyrithian cross section from continuous, coherent tapes and ribbons.

Accordingly, it is the principal object of this invention to provide a process for preparing filamentary microtapes of labyrinthian cross section, which process provides substantially rigid control of the microtape width and denier.

It is a further object to provide such a process utilizing a tape or ribbon of an organic, thermoplastic, resinous material.

It is a still further object of the invention to provide such a process which is utilizable with fused, unoriented tapes or ribbons.

The above and related objects are achieved by means of the process comprising the passing of a fused, unoriented, supercooled, continuous, coherent tape or ribbon of an organic, thermoplastic, resinous material through restricting means of narrower Width than the width of said tape or ribbon while maintaining said tape or ribbon under sufficient tension to cause orientation essentially simultaneously with the shaping of the microtape and withdrawing the shaped microtape from said restricting means at an anlge of at least 15 degrees from the straight line projection of the ribbon through and past the restricting means and no greater than 15 degrees measured from a vertical plane through the path of said ribbon at its point of departure from said means.

The tapes useful in the present method may be of any organic, thermoplastic, resinous material. As materials which may be advantageously used are the normally crystalline polymeric materials. These are the polymers which have a tendency to form crystallites or sites where small segments of a plurality of the polymer chains are oriented and held in position by secondary valence forces. This crystallite formation or crystallinity is usually visible when the polymers are examined by X-ray diffraction. Typical of the normally crystalline polymeric materials falling within the advantageous definition are the polymers and copolymers of at least 70 percent by weight of vinylidene chloride with any remainder composed of one or more other monoethylenically unsaturated comonomers exemplary of which are vinyl chloride, vinyl acetate, vinyl propionate, acrylonitrile, alkyl and aralkyl acrylates having alkyl and aralkyl' groups of up to about 8 carbon atoms,

acrylic acid, acrylamide, vinyl alkyl ethers, vinyl alkyl ketones, acrolein, allyl esters and ethers, butadiene and chloroprene. Known ternary compositions also may be employed advantageously. Representative of such polymers are those composed of at least 70 percent by weight of vinylidene chloride with the remainder made up of, for example, acrolein and vinyl chloride, acrylic acid and acrylonitrile, alkyl acrylates and alkyl methacrylates, acrylonitrile and butadiene, acrylonitrile and itaconic acid, acrylonitrile and vinyl acetate, vinyl propion'ate or vinyl chloride, allyl esters or ethers and vinyl chloride, bntadi ene and vinyl acetate, vinyl propionate, or vinyl chloride and vinyl ethers and vinyl chloride. Quaternary polymers of similar monomeric composition will also be known.

Lerner :2

t; It has been found that the normally crystalline copolymers composed of from about 92 to 99 percent by weight of vinylidene chloride, and, correspondingly, from 8 to 1 percent by weight of acrylonitrile or of a lower allryl acrylate have suitable polymerization characteristics, are well adapted for use in the manipulative steps in this process, and result in exceptionally useful filamentary articles. For these reasons, these vinylidene chlorideacrylonitrile and vinylidene chloride-lower alkyl acrylate copolymers represent preferred species for use herein. it should be understood, however, that the process is not limited to the treatment of tapes and ribbons of normally crystalline polymers but that those formed from any uonelastic, polymeric material may be used. There are many materials, such as polyvinyl chloride and polystyrene, which are capable of forming continuous, coherent articles which are orientable but do not normally form crystallites. The polymeric materials, whether crystalline or noncrystalline, may also include minor amounts of monomers,

such as vinyl pyrrolidone, vinyl oxazolidinone, vinyl alkyl oxazolidinone, and the like, which are known to aid the dye-receptivity and other properties of fibrous materials. Likewise, it is possible for the polymers to contain interpolymerized light and heat stabilizers. Also operable in the present method are tapes and ribbons of polymeric materials, such as the polyolefins, including, for example, polyethylene, polypropylene, copolymers of ethylene and propylene, and polyisobutylene. Equally useful in the method are the tapes and ribbons formed from condensation polymers, such as the polyamides, including polyhexamethylene diadipamide, and the polyesters, including polyethyleneterephthalate. Also of utility are the tapes and ribbons of rubber hydrochloride and thermoplastic synthetic cellulose derivatives, including cellulose esters, such as cellulose acetate and cellulose others, such as methyl cellulose and hydroxypropyl methyl cellulose. It should be apparent that any organic, thermoplastic, resinous material which is capable of being formed into a flat tape or ribbon will find utility in the present invention.

The useful tapes for the present method are flexible tapes usually of about 0.001 to 0.005 inch in thickness and of about 0.1 to 1 inch inwidth. The thickness and width to be used in any given instance will depend in large measure upon the end product desired. The above limits are those which would normally be associated with the manufacture of filamentary microtapes to be used in conventional textile fabrics. When it is desired to make filamentary microtapes of greater size than, for example, about 0.3 inch, it would usually be found desirable to employ other known fabrication means, such as thermal extrusion for their preparation. Wide sections of tape which are more accurately referred to as films are not handled conveniently in the present procedural steps. However, it should be understood that the process is not limited precisely to the 1-inch maximum, since useful articles may be prepared herefrorn, although with less control of width than with the narrower tapes.

As mentioned, the method of the present invention involves the passage through a particular path of a flat, fused, unoriented tape in planar fashion through confining and restricting means to cause the desired labyrinthian cross section. By that it is meant that these means are of smaller dimension than the width of the flat tape passed therethrough. The confining and restricting means may take any given form wherein the cross-sectional area through which the tape passes is narrower than the fiat tape itself. A particularly convenient and accordingly preferred means is a groove in a rigid shaping device. With any given flat tape the shape and dimensions of the groove determine in large measure the shape and final dimensions of the microtape. The significance of this point will become more apparent as the description of the invention proceeds.

The advantages and benefits, as well as the operation of the herein claimed process, will be more apparent from the following description and the appended drawing which illustrates a preferred procedural sequence for carrying out the process. in the drawings:

FIGURE 1 represents an end elevation,

FIGURE 2 represents a side elevation of a useful grooved shoe,

FIGURES 3-5 represent typical groove sections,

FIGURE 6 represents a preferred embodiment of the grooved shoe,

FIGURE 7 represents a preferred groove configuration, and

FEGURE 8 represents schematically a typical procedural sequence for carrying out the process.

In the embodiment illustrated in FIGURE 8, a flat, fused tape it) or ribbon is fed through a suitable guide l1, around a first pair of snubbing rolls l2, and then through a groove located in a shaping device such as a stationary grooved shoe 13. The tape 10 or ribbon is then passed around a second pair of snubbing rolls 14 which maintains the tape 10 or ribbon under sufficient tension to cause orientation of the tape 10 or ribbon. Finally, the oriented microtape is wound on suitable collecting means 15.

The peripheral speeds of the snubbing rolls (l2, 14) to be used depend in large measure upon the polymer used in forming the tape 10. With the preferred normally crystalline vinylidene chloride polymers, this ratio must be at least 2 to l and preferably should be about 4 to l to be beyond the elastic limit of the polymer. Stretch ratios and therefore peripheral speeds to be used with other organic, thermoplastic, resinous materials will be known or may be determined by simple preliminary experiment.

The shaping of microtape occurs in a stationary grooved shoe, such as that illustrated in FIGURES 1 and 2 having grooves in a convex curvilinear surface. When driven, the rolls should rotate in the same direction as the ribbon and at a peripheral speed that is about the same as the rate of travel of the ribbon. For purposes of simplicity, the description of the illustrated embodiment will be limited to the stationary shoe but the same considerations apply to the grooved roll or other equivalent.

The shape of the groove in the shoe determines to large extent the type of folding which occurs and, combined with the dimensions of the groove relative to the tape, determines the amount of folding or rolling that occurs. Typical grooves which provide the desired folding in the present invention are illustrated in FIGURES 3, 4, 5 and 6 of the appended drawing. In general, it has been found that grooves with divergent side walls, such as those of FIGURES 2-4, tend to encourage edge curling while grooves with parallel walls, such as that of FIGURE 5, tend to cause folding of the edge portions back upon the tape. Also as a general guide, the shape and dimensions of the bottom or root of the groove influences the resultant product. Thus, a flat bottomed groove (FIGURE 3) having divergent side walls wherein the bottom is a small fraction of the width of the "fiat tape used will encourage the production of a microtape'having tightly rolled edges with the rolled edges touching. As the width of the groove root is increased, the resulting microtapes will tend to have the curled edges more proportionately separated until a point is reached where the microtape, when magnified, will have the cross-sectional appearance of a ribbon with curled beaded edges. As the divergence of the groove walls approaches parallel, there is a tendency for a combination of folding and curling to occur. This eifect can also be attained with a groove of configuration, such as that of FlGURE 4. In this effect, there is a small amount of curling at the extremities of the tape and the tape then folded back upon itself, It should be apparent that the process and apparatus is subject to the preparation of a Wide variety of cross-sectional configuration. Judicious selection of groove shape and dimension, as well as of procedural conditions that will result in the desired microtape, can be made with but a few simple preliminary experiments.

It has been found that with some polymeric materials it is desirable to heat the shaping device slightly to assist in the rolling or folding. Usually temperatures of not over about 100 C. will suffice for this purpose. Means for heating the shoe or the grooved roll will be known.

It has been found that maximum mechanical effect is obtained when the tape enters the groove at somewhat of an are as opposed to a tangential entry. To achieve such an effect with the stationary shoe, a rod or bar may be affixed to the shoe to bridge the groove transversely. When the tape is passed over the bar into the shoe, the preferred angle of entry will be obtained.

An embodiment which is preferred is the use of a tapered groove of diminishing cross-sectional area. This permits a progressive reduction in area of the restricting means and results in more controllable and orderly folding of the tape or ribbon. This embodiment is illustrated in FIGURE 7.

It should be apparent that reproducibility of the microtape shape is obtained only when the dimensions of the fused, fiat tape are essentially constant and the shaping conditions, such as the level at which the tape enters the groove, the depth to which it travels within the groove, and other factors, are maintained substantially constant. These constant conditions are easily attained by use of the aforementioned bar affixed to the shoe and further by drawing the tape through the grooved shoe under substantially constant forwarding tension. This forwarding tension is attained with the second set of snubbing rolls.

The microtape must be drawn off the grooved shoe 13 at an acute angle (angle or in FIGURE 6) if the stated objectives of the invention are to be realized. It has been found that this deflection of the path of the tape is necessary if microtapes of uniform width are to be achieved. It has also been found that the angular deflection must be at least 15 degrees from the straight line projection (line X in FIGURE 6) of the path of the tape. When that angle is less than 15 degrees, the folding is irregular and non-uniform and the process is non-reproducible and erratic. Further, the angle should not exceed an angle in FIGURE 6) of degrees measured from a vertical plane through the path of said tape at its point of departure from the restricting means. If the deflection trespasses within that latter 15 degree area (angle 6 in FIGURE 6), an undue stress is placed on the emerging microtape which may result in breakage and fibrillation. Preferably, the angle of deflection (a in FIGURE 6) should be from '15 to degrees from the projected path to attain best results with the least amount of strain imposed on the microtape. Because of this angular withdrawal, it is virtually mandatory that the trailing edge of the groove in the shoe (represented as A) be rounded with a curvature of very small radius of the order of about inch. This lessens the stress applied to the microtape by the preferred withdrawal.

As mentioned, the process of the present invention permits the preparation of the microtapes from previously fused but unoriented tapes or ribbons. This process results in several benefits. It is capable of continuous operation and is capable of being fitted into an integrated scheme that would include the tape or ribbonmaking procedural sequence immediately preceding the present process. The microtapes resulting from the process of this invention are characterized by a higher tenacity and a better hand than the tapes or ribbons from which they are formed. The microtapes are further characterized by uniform width and denier and by the absence of any frayed, uneven, or torn edges.

-By means of the present method and apparatus, it is 6 possible to prepare microtapes of a wide variation in width/thickness ratio. Thus, microtapes having a width which is about two times greater than its thickness may be prepared with little deviation in this ratio. Such a filament will approximate the known monofilaments and fibers of oval cross section. However, with the same apparatus and with minor change in conditions the width/thickness ratio may be changed to 10 to 1 or greater. By merely changing the groove size, it is possible to attain width/ thickness ratios of 30 to 1 or higher. Microtapes of such width/thickness ratios closely approximate fine ribbons or tapes and yet are subject to unusually exact control of width and denier and have edges which are non-frayable and have high tear strength.

The present process also is readily adaptable to the production of tapes of different deniers with minimum change in apparatus and conditions. When two or more flat tapes or ribbons are stacked and passed through the herein claimed procedural sequence, there results a microtape of similar configuration to that of a single tape but with proportionately increased thickness and denier. The width of the so-laminated or plied tapes is relatively modestly increased over that of the single, flat tape.

It will be appreciated that width/thickness ratios, denier, and cross-sectional configuration may be infiuenced by tape width and thickness, as well as the above-mentioned factors. The tape width can be adjusted with the slitting means or to a significant extent within limits by hot stretching the flat tape during or subsequent to fusion. Tape thickness can be varied during its preparation or by the aforementioned plying technique.

It can thus be seen that the process is susceptible in flexibility of operation to a diversity of microtape crosssectional configurations, deniers, and width/ thickness ratios without the major retooling required by the prior known filament-making process when any change is contemplated.

The operation of the method of the process will be more apparent from the following illustrative example wherein all parts and percentages are by weight.

Example A ribbon prepared by the continuous coagulation of a latex of a copolymer of 97 percent vinylidene chloride and 3 percent acrylonitrile into a coagulum followed by fusion of the coagulum was made having a thickness of 0.0021 inch and a width of inch. After fusion, the ribbon was supercooled by passage over chilled rolls. The supercooled ribbons were passed through snubbing rolls at a rate of 26 feet per minute, then in register through grooves cut into a stationary shoe, each groove being inch wide and having divergent sides with a rectangular section cut into the bottom. The travel of the ribbons was such that they contacted the grooved shoe. The shoe was heated internally with an electric heater to maintain the temperature of the surface at about C. The ribbons were withdrawn from the grooves at an angle of about degrees to the projection of the path of the tape. The ribbons then passed through a second pair of snubbing rolls operated at a peripheral speed to stretch the ribbons to about four times the length entering the grooves. The resulting ribbon was found to have a transverse section folded back upon itself four times with a thickness of 0.0038 inch and a width of 0.0301 inch.

Similar results were obtained when the ribbons were withdrawn at any angle a between 15 to 60 degrees.

When the process was repeated without orienting the ribbon in the groove, the resultant microtape reopened before winding on cores.

By Way of contrast, the tapes were passed through the grooves in the shoe without the angular deflection. In most instances, the ribbon rotated degrees and passed through the groove edgewise without any folding. In the remaining instances, a small amount of non-uni- C form folding occurred at one edge. In addition, when the angular deflection Was about 15 degrees (6 equals 75 degrees), the folding was erratic, non-uniform, and generally unacceptable from a textile fiber viewpoint. When the tapes were passed through the grooves with angle 6 at 15 degrees or less, the tapes broke frequently.

Linear polyethylene ribbons were formed into microtapes using the process above except that the grooved shaping device Was heated to about 120 C.

What is claimed is:

1. A process for preparing microtapes of labyrinthian cross section characterized in having a width that is at least two times greater than its thickness, said process comprising the passing of fused, unoriented, supercooled, continuous, coherent ribbon of an organic, thermoplastic, resinous material through open sided restricting means of narrower width than the width of said ribbon While maintaining said ribbon under sufficient tension to cause orientation, said ribbon being withdrawn downwardly from said restricting means at an angle of at least 15 degrees from the straight line projection of the ribbon through and past the restricting means and no greater than 15 degrees measured from a vertical plane through the path of said ribbon at its point of departure from said means.

2. The process claimed in claim 1 wherein said organic, thermoplastic, resinous material is a normally crystalline polymeric material.

3. The process claimed in claim 2 wherein said normally crystalline polymeric material is a vinylidene chloride polymer composed of at least 70 percent by weight vinylidene chloride with any remainder of at least one monoethylenically unsaturated comonomer.

4. The process claimed in claim 3 wherein said vinylidene chloride polymer is a copolymer of vinylidene chloride and acrylonitrile.

5. The process claimed in claim 3 wherein said vinylidene chloride polymer is a copolymer of vinylidene chloride and an alkyl acrylate having from 1 to 8 carbon atoms in the alkyl group.

6. The process claimed in claim 1 wherein said ribbon is about 0.001 to 0.005 inch in thickness and from 0.1 to 1 inch in Width.

7. The process claimed in claim 1 wherein said organic, thermoplastic, resinous material is a solid polyolefin.

8. The process claimed in claim 7 wherein said solid polyolenn is polyethylene.

9. The process claimed in claim 7 wherein said solid polyolefin is polypropylene.

References ited UNITED STATES PATENTS 2,041,798 5/1936 Taylor 161-177 X 2,240,274 4/1941 \Nade.

2,615,491 10/1952 Harris et al. 161178 X 2,981,052 4/1961 MacHenry 57-165 X 2,985,503 5/1961 Becker 264-210 X 3,001,354 9/1961 Davis 57-165 X 3,077,004 2/1963 Mummery 264103 X ALEXANDER H. BRODMERKEL, Primary Examiner. DONALD J. ARNOLD, Examiner.

I. H. WOO, Assistant Examiner. 

